1. Field of the Invention
The present invention relates to an addition curable silicone resin composition for a light emitting diode (LED), and relates particularly to an addition curable silicone resin material that yields a cured product which exhibits excellent transparency, is ideal for protecting light emitting diode elements, altering or regulating wavelength, or acting as a lens component material, and exhibits favorable crack resistance even under conditions involving high temperature/low temperature cycling.
2. Description of the Prior Art
It is well known that when LEDs are activated and lit, a rapid rise in temperature occurs, subjecting the LED element to a thermal shock. Accordingly, when an LED element is turned on and off repeatedly, the LED element is exposed to severe temperature cycles.
Epoxy resins are generally used as the sealing materials for LED elements. However, because epoxy resins have a high elastic modulus, the bonding wires are subjected to stress and may break as a result of temperature cycling, and cracks may develop within the epoxy resin. Furthermore, as a result of the stress applied by the epoxy resin to the LED chip, there is also a risk of a deterioration in the light emission efficiency caused by destruction of the crystal structure of the semiconductor material. As a countermeasure to these problems, a method that uses a room-temperature curable silicone rubber as a buffer material, wherein the exterior of this rubber is then sealed with an epoxy resin, is now established as an accepted method. However, with this method, because the epoxy resin does not adhere to the silicone rubber, temperature cycling leads to peeling at the interface between the epoxy resin and the silicone rubber, and it is known that the light extraction efficiency deteriorates dramatically over time. The use of silicone resins as alternative materials to epoxy resins has also been proposed (patent references 1, 2 and 3). Because silicone resins exhibit comparatively superior heat resistance, weather resistance and color fastness when compared with epoxy resins, in recent years, LED examples that use silicone resins, primarily with blue LEDs and white LEDs, have become more prevalent. However, although these silicone resins have a lower elastic modulus than epoxy resins, their mechanical properties such as their flexural strength are inferior, meaning they suffer from a tendency for cracks to occur as a result of thermal shock generated during the turning on and off of the LED.
[Patent Reference 1] JP 11-1619 A
[Patent Reference 2] US 2002-0161140 A1
[Patent Reference 3] US 2004-0116640 A1